So I'm a newbie but very tech-savvy. I bought a 2007 Stern SM and installed a Stern SM Rev A Shaker Motor kit. After a couple installation glitches, all fine for about half a dozen games. Suddenly, mid-game the shaker motor starts (properly, in response to play field activation) but didn't stop and now runs whenever power is applied to the machine. Any clues?

LTG - thanks. That was my thought, too. Question is, is it the transistor on the SM PCB or the transistor on the I/O board? What would your guess be?

LTG - Many thanks. I'm not the best at desoldering/soldering. Don't suppose there's any alternative I haven't heard of?

LTG - Thanks!

coz6 - Thanks

UPDATE. Finally got around to replacing the I/O PCB transistor associated with the SM. Once again, as soon as power applied the motor runs. I'm emailing with Stern Tech support and waiting for reply but it seems obvious that it's probably the SM PCB.

Many thanks Krupps4!

Arghh!!!! So Stern sent a new Shaker Motor PCB - that fixed the problem - for 2 games!!! Once again, motor runs continuously. The problem is obviously the motor PCB but why the premature failures? Krupps4, I guess it's possible they sent another weak board but could there be anything else causing the board failure?